reCAPTCHA supplies subscribing websites with images of words that optical character recognition software has been unable to read. The subscribing websites (whose purpose is generally unrelated to the book digitization project) present these images for humans to decipher as CAPTCHA words, as part of their normal validation procedures. They then return the results to the reCAPTCHA service, thereby contributing to the digitization project. The result is that the university receives approximately 3,000 man hours per day of free labor to help in the preservation of books.I always thought those words with squiggly lines were just especially clever CAPTCHA tests; I had no idea they were actually part of an incredibly cool distributed processing scheme. Spammers, of course, have learned how to use a reversed version of this system where a program entices real humans to decipher CAPTCHAs, in return for which they get to view racy images for free.